import singleton as patterns

class Command(object):
def do(self):
CommandHistory().append(self)

def undo(self):
pass

def redo(self):
pass

def __str__(self):
return 'command'


class CommandHistory:
__metaclass__ = patterns.Singleton

def __init__(self):
self.__history = []
self.__future = []

def append(self, command):
self.__history.append(command)
del self.__future[:]

def undo(self, *args):
if self.__history:
command = self.__history.pop()
command.undo()
self.__future.append(command)

def redo(self, *args):
if self.__future:
command = self.__future.pop()
command.redo()
self.__history.append(command)

def clear(self):
del self.__history[:]
del self.__future[:]

def hasHistory(self):
return self.__history

def getHistory(self):
return self.__history

def hasFuture(self):
return self.__future

def getFuture(self):
return self.__future

def _extendLabel(self, label, commandList):
if commandList:
commandName = u' %s'%commandList[-1]
label += commandName.lower()
return label

def undostr(self, label='Undo'):
return self._extendLabel(label, self.__history)

def redostr(self, label='Redo'):
return self._extendLabel(label, self.__future)